我有這個對象列表List<DetailDto> details; @Value public class DetailDto implements Serializable { String category1; Integer category2; Integer price; transient Integer totalPrice; }有了這份清單[ { "category1": "ABC", "category2": 30, "price": 195, "totalPrice": null }, { "category1": "ABC", "category2": 30, "price": 195, "totalPrice": null }, { "category1": "ABC", "category2": 30, "price": 195, "totalPrice": null }, { "category1": "ABC", "category2": 30, "price": 390, "totalPrice": null }, { "category1": "ABC", "category2": 30, "price": 390, "totalPrice": null }, { "category1": "DEF", "category2": 30, "price": 455, "totalPrice": null }, { "category1": "DEF", "category2": 30, "price": 455, "totalPrice": null }, { "category1": "DEF", "category2": 30, "price": 455, "totalPrice": null }, { "category1": "DEF", "category2": 30, "price": 455, "totalPrice": null }, { "category1": "GHI", "category2": 1, "price": 18000, "totalPrice": null }]我想通過將字段List<DetailDto>總結為條件為的字段來制作另一個對象：pricetotalPrice字符串category1很常見整數category2很常見整數price很常見在這一點上我有這個List<List<DetailDto>> summarizedList = detail().stream() .collect(Collectors.groupingBy(DetailDto::category1, Collectors.groupingBy(DetailDto::category2, Collectors.groupingBy(DetailDto::price)))) .values() .stream() .flatMap(c1 -> c1.values().stream()) .flatMap(c2 -> c2.values().stream()) .collect(Collectors.toList());返回我List<List<DetailDto>>而且我不知道如何使它正確，在我嘗試這個之后summarizedList.stream().map(dto -> dto.stream().reduce((x,y) -> new DetailDto(x.productCode(), x.productQt(), x.orderPrice(), Integer.sum(x.orderPrice(), y.orderPrice()).orElse(null).collect(Collectors.toList());你們能幫幫我嗎？
1 回答
白豬掌柜的
TA貢獻1893條經驗 獲得超10個贊
這是一種可能性：使用復合鍵一次分組：
.collect(Collectors.groupingBy(DetailDto::key, Collectors.summarizingInt(DetailDto::getPrice)))
請參閱KeyDetailDto.java 中的定義（并注意其 eclipse 生成hashCode的equals方法）：
import java.io.Serializable;
@SuppressWarnings("serial")
public class DetailDto implements Serializable {
String category1;
Integer category2;
Integer price;
transient Integer totalPrice;
public DetailDto() {
}
public DetailDto(String category1, Integer category2, Integer price, Integer totalPrice) {
super();
this.category1 = category1;
this.category2 = category2;
this.price = price;
this.totalPrice = totalPrice;
}
public String getCategory1() {
return category1;
}
public void setCategory1(String category1) {
this.category1 = category1;
}
public Integer getCategory2() {
return category2;
}
public void setCategory2(Integer category2) {
this.category2 = category2;
}
public Integer getPrice() {
return price;
}
public void setPrice(Integer price) {
this.price = price;
}
public Integer getTotalPrice() {
return totalPrice;
}
public void setTotalPrice(Integer totalPrice) {
this.totalPrice = totalPrice;
}
Key key() {
return new Key(category1, category2, price);
}
}
class Key {
String category1;
Integer category2;
Integer price;
public Key(String category1, Integer category2, Integer price) {
super();
this.category1 = category1;
this.category2 = category2;
this.price = price;
}
public String getCategory1() {
return category1;
}
public Integer getCategory2() {
return category2;
}
public Integer getPrice() {
return price;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((category1 == null) ? 0 : category1.hashCode());
result = prime * result + ((category2 == null) ? 0 : category2.hashCode());
result = prime * result + ((price == null) ? 0 : price.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Key other = (Key) obj;
if (category1 == null) {
if (other.category1 != null)
return false;
} else if (!category1.equals(other.category1))
return false;
if (category2 == null) {
if (other.category2 != null)
return false;
} else if (!category2.equals(other.category2))
return false;
if (price == null) {
if (other.price != null)
return false;
} else if (!price.equals(other.price))
return false;
return true;
}
}
Main.java
import java.io.IOException;
import java.util.IntSummaryStatistics;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;
public class Main {
public static void main(String[] args) throws IOException {
DetailDto[] values = new ObjectMapper().readerFor(DetailDto[].class)
.readValue(Main.class.getResourceAsStream("data.json"));
// for (DetailDto dto : values) {
// display(dto);
// }
Map<Key, IntSummaryStatistics> res = Stream.of(values)
.collect(Collectors.groupingBy(DetailDto::key, Collectors.summarizingInt(DetailDto::getPrice)));
Stream<DetailDto> agg = res.entrySet().stream().map(e -> new DetailDto(e.getKey().category1,
e.getKey().category2, e.getKey().price, (int) e.getValue().getSum()));
agg.forEach(Main::display);
}
protected static void display(DetailDto dto) {
final ObjectWriter json = new ObjectMapper().writerFor(DetailDto.class).withDefaultPrettyPrinter();
try {
System.out.println(json.writeValueAsString(dto));
} catch (JsonProcessingException e) {
throw new RuntimeException(e);
}
}
}
！
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